1. Field of the Invention
The present invention relates to fluidic, electrical, electronic, and optical flex circuits and connections thereto.
2. Background of the Invention
Flex circuits, also known as flexible circuits, flexible printed circuit boards, and flexible printed wiring, are circuits made in or on flexible substrates, which substrates are substantially planar in shape. The flexible substrates may be bent and folded in order to accommodate three-dimensional shape requirements.
Flex circuits were first described by Albert Hanson of Berlin, Germany in British Patent 4,681 issued in 1903. The patent is noted in “Flexible Circuitry—Technology Background and Important Fundamental Issues”by Joseph Fjelstad, available on the internet at http://www.tessera.com/library.cfm, which article also provides a good overview of electrical flex circuit technologies. Further overview material on flex circuits is provided by the same author, Joseph C. Fjelstad, Pacific Consultants LLC, Mountain View, Calif., in “Tutorial: An Overview of Flexible Printed Circuit Technology,”Chip Scale Review Online, January-February 2001, available as a link on the internet at    http://www.chipscalereview.com/issues/0101/homeissue.html and given in full at    http://www.chipscalereview.com/issues/0101/tutorial—01.html.
Hanson's 1903 patent described the production of flexible flat conductors on a sheet of insulating paraffin-coated paper. Today, flex circuits are typically made using polyimide such as DuPont® Kapton™ as the flexible insulating material, although many other materials including paper, polyamide, polyester terephthalate (PET), random-fiber aramid (Nomex), and polyvinyl chloride (PVC) may be used. Embedded within or upon the flex circuit can be electrical leads and electrical devices such as microchips. Recessed within the surface of the flex circuit can be fluid wells and trenches, while embedded within the flex circuit can be fluid capillary channels. Embedded within or upon the flex circuit can also be optical devices including fiber optic elements, optical gratings, optical sources, and optical receivers. If the flex circuit has only electrical leads it is often called an electrical flex circuit, while if it has fluid wells, trenches, or capillary channels it is often called a fluid flex circuit or a microfluidic circuit. If it has optical elements it can be called an optical flex circuit or a flexible optical circuit; see, for example, U.S. Pat. Nos. 5,902,435; 6,005,991; 6,069,991; 6,088,498; and 6,222,976. Fluid flex circuits and microfluidic circuits can include electrical elements; see, for example, U.S. Pat. Nos. 5,645,702; 5,658,413; 5,804;022; 5,882,571; and 6,093,362. The advantageous three-dimensional nature of flex circuitry is well known. See, for example, U.S. Pat. No. 4,928,206, “Foldable Printed Circuit Board.”
Connecting an external electrical, fluid, or optical path to a flex circuit typically requires entering the plane of the flex circuit from some out-of-plane direction. This simple objective has historically been very challenging and has required complex structures. See, for example, U.S. Pat. Nos. 6,033,628; and 6,194,900 in which the connectors to a flexible fluid circuit substrate require separate assembly.
The problem of fluid interconnections has been addressed by Hans-Peter Zimmerman (see, e.g., U.S. patent application Ser. No. 09/570,948, application date May 15, 2000 entitled “Coupling to Microstructures for a Laboratory Microchip”). Zimmerman describes flexible structures that can bend out of the plane of a flexible substrate, but the bending of such structures is only simple cantilever bending. One disadvantage associated with simple cantilever bending is that it is impossible, for example, to space sample introduction siphons at the 4.5 mm well spacing centers of a standard 384-well microtiter plate, because the 12 mm reach required is greater than the 4.5 mm spacing so that there is simply no room to place all of the required cantilever siphons. In order to get dense interconnections an improved structure is required.
Flex circuits have been fabricated incorporating bending structures that are more complicated than simple cantilevers. For example, U.S. Pat. No. 4,587,719 by the present inventor describes a method of folding a polyimide flex circuit that results in a structure that remains in the original plane of the flex circuit. However, the U.S. Pat. No. 4,587,719 does not teach a method or apparatus for reaching out of the plane of the circuit, nor does it teach any method or apparatus for out-of-plane interconnection.
Regarding electrical interconnections, several schemes are presented in U.S. Pat. Nos. 4,961,709; 5,197,889; 5,452,182; 5,812,378; 5,859,472; 5,900,674; 5,938,452; 5,973,394; 6,029,344; 6,033,433; 6,046,410; 6,092,280; and RE34084 for achieving dense interconnections between circuits, but none of these schemes exhibit the simplicity of fabrication that can be obtained if the interconnection structure can be fabricated within the structure of the flex circuit.
Regarding optical interconnections, the art of optical flex circuits is fairly young in development. See, for example, U.S. Pat. Nos. 5,835,646; 5,902,435; 5,981,064; 6,005,991; 6,069,991; 6,088,498; 6,091,874; and 6,097,871. However, the art of optical interconnections does not provide solutions for simple and dense optical interconnections between face-to-face adjacent planar optical flex circuits. It is often most important in an optical interconnect to avoid losing the light from a fiber due to bending or kinking of the fiber. It is of secondary importance to achieve a long reach from the substrate plane.
Planar springs are taught to some degree in U.S. Pat. Nos. 3,950,846; 3,968,336; 3,979,568; 4,066,860; 4,548,086; 4,919,403; 5,082,997; 5,525,845; 5,555,972; and 5,673,785. In particular a planar spiral spring extending out of the plane of the substrate is taught in U.S. Pat. Nos. 4,066,860 and 5,673,785. However, the patents do not teach or allude to isolating an electrical lead or other conveying element on or in the spring. Additionally, the spring cannot be extended to a distance greater than the width of the spring.
Thus, there still exists a need for a flexible structure that can reach out of the plane of a flexible substrate, for purposes of interconnection and sample transfer, which can be spaced on the flexible substrate at a center-to-center distance smaller than the distance by which it reaches out of the plane, and which is simple to fabricate.